1. Field of the Invention
This invention relates to a liquid dispenser, more particularly to a liquid dispenser adapted to be connected to a container for dispensing a liquid from the container.
2. Description of the Related Art
FIGS. 1 and 2 illustrate a conventional liquid dispenser 10. The liquid dispenser 10 is to be connected to a container (not shown) for dispensing a liquid from the container. The liquid dispenser 10 includes a hollow shank 11 having a fluid chamber 111. A hollow piston rod 12 extends inside the shank 11, and has a fluid passage 121 extending therein and a stopper 122 to confine the movement of the piston rod 12 in the shank 11. An upper spring 13 seated on the stopper 122 is sleeved around the piston rod 12 to urge downward a hollow piston 14 which is also sleeved around the piston rod 12 below the upper spring 13. The piston 14 has a contacting part 141 in sliding contact with an outer surface of the piston rod 12. A spring seat 15 includes a radially extending flange portion 153 and an upper hollow tubular portion 151 extending upward from the flange portion 153 into a bottom hole 123 in the piston rod 12. The bottom hole 123 receives the tubular portion 151 in a way that it is in intimate contact with the tubular portion 151. The tubular portion 151 is provided with a fluid aperture 152 adjacent to the flange portion 153 for communication with the fluid passage 131. The flange portion 153 abuts against a skirt portion 142 of the piston 14 to seal releasably the aperture 152. Referring now to FIG. 3, as the piston rod 12 is pressed downward, the piston 14 is pushed upward by the fluid inside the fluid chamber 111 to move away from the skirt portion 142 and to place the aperture 152 in communication with the fluid chamber 111 so that the fluid inside the fluid chamber 111 can be dispensed out of the liquid dispenser 10. It is noted that, since the tubular portion 151 of the spring seat 15 is required to be in tight contact with the bottom hole 123 in the piston rod 12, and since the spring seat 15 and the piston rod 12 are both made from a rigid plastic material, the insertion of the former into the latter during assembly can become difficult, and breakage of both parts may occur. Moreover, it is not easy to completely eliminate the air in the bottom hole 123 upon insertion of the piston rod 12, thereby resulting in an incorrect positioning of the latter.
FIGS. 4 and 5 illustrate another conventional liquid dispenser 20. The liquid dispenser 20 includes a hollow shank 21 having a fluid chamber 211. A hollow piston rod 22 extends into the shank 21, and has a fluid passage 221 extending therein, a stopper 223 to confine the movement of the piston rod 22, and a fluid aperture 222 near a bottom portion of the piston rod 22 for communication with the fluid passage 221. An upper spring 23 seated on the stopper 223 is sleeved around the piston rod 22 to urge downward a hollow piston 24 which is also sleeved movably around the piston rod 22 below the upper spring 23. The piston 24 includes a contacting portion 241 in sliding contact with the piston rod 22 to enclose sealingly the aperture 222. A spring seat 25 is sleeved around the bottom portion of the piston rod 22, and is seated and urged by a lower spring 26. The spring seat 25 has an axially extending through-hole 251 confined by an inner surface 252 which encloses tightly the bottom portion of the piston rod 22 so that the spring seat 25 may move along the piston rod 22. Referring now to FIG. 6, as the piston rod 22 is pressed downward, the piston 24 is pushed upward via the fluid inside the chamber 211 to move away from the spring seat 25 and to place the aperture 222 in communication with the fluid chamber 211, thereby dispensing the fluid out of the liquid dispenser 20. However, the spring seat 25 is bound to the bottom portion of the piston rod 22 only via the intimate contact of the inner surface 252 with the bottom portion of the piston rod 22, such contact may become loosened and the spring seat 25 may be moved away from its binding place due to an unbalanced force acting on the spring seat 25 by virtue of the lower spring 26 and the upper spring 23. Since the piston 24 abuts against the spring seat 23, it may be misplaced, as a result of the above described unbalanced force, to a position that can cause leakage of the fluid or hinder movement of the piston 24 to move to the position that places the aperture 222 in communication with the fluid chamber 211 upon pressing of the piston rod 22.
FIGS. 7 and 8 further illustrate another conventional liquid dispenser 30. The liquid dispenser 30 includes a hollow shank 31 having a fluid chamber 311. A hollow piston rod 32 extends into the shank 31, and has a fluid passage 321 extending therein, a bottom hole 323, and a radially extending stopper 322 adjacent to the bottom hole 323. A spring seat 33 urged by a lower spring 35 includes a top hollow tubular portion 331 extending upwardly into the bottom hole 323, a downwardly extending bottom portion 334 extending downward into the lower spring 35, and a radially extending flange 333 seated by the lower spring 35 and extending upward from the bottom portion 334. A fluid aperture 332 is provided in the bottom of the tubular portion 331 to communicate with the fluid passage 321. A hollow tapered piston 34 is disposed between the piston rod 32 and the spring seat 33, and includes a top end portion 341 abutting sealingly against the stopper 322 and a skirt portion 343 extending downward from the top end portion 341 and receiving the flange 333 therein. A radially extending shoulder 342 extends from the skirt portion 343 to seat sealingly on the flange 333 and seal releasably the aperture 332. Referring now to FIG. 9, as the piston rod 32 is pressed downward, the shoulder 342 of the piston 34, which is made from a soft plastic material, is pushed upward by the fluid under it, thereby flexing the shoulder 342. Such flexing will move the shoulder 342 away from the flange 333 to place the aperture in communication with the fluid chamber 311. However, since the piston 34 is made from soft plastic material, it tends to degrade easily because of the expansion and contraction of the plastic material due to the affect of the weather, thereby arising in poor sealing at the shoulder 342.